Method of and apparatus for utilizing radioactive materials for generating electrical energy



e t. 8 1953 E. e. LINDER 2 651 730 h p METHOD OF AND APPARATUS FOR UTILIZING RADIOACTIVE MATERIALS FOR GENERATING ELECTRICAL ENERGY Filed March 30. 1949 Patented Sept. 8, i953 UETE Ernest G. Linder, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 30, 1949, Serial No. 84,344

This invention relates generally to the generation of electrical energy and more particularly to unique methods of and means for deriving and utilizing a plurality of electrical energies originating in a single source of nuclear reactions.

The enormous magnitudes of energy provided by certain nuclear reactions of radioactive substances provide a tremendous field for the de velopment of new sources of electrical energy. Since some radioactive radiations (energy) are largely electrical in nature, it is desirable that such energy be converted directly to electrical energy of usable form. The al-phaparticle and beta-particle emissions from certain radioactive substances comprise positively or negatively charged particle rays, respectively, having energies which vary from low values to several million electron volts. For example, alpha-ray emission comprises positively charged particles having energies varying from zero to the order of ten million electron volts, while beta-particle emission com-prises negatively charged particles having energies varying from low values to the order of three million electron volts. The direct utilization of the high electrical potentials which may be derived from such charged particles provides much more convenient and efiicient utilization of nuclear energy than previously proposed systems wherein the nuclear energy is converted to thermal energy, the thermal energy then converted to mechanical energy, and the mechanical energy then converted to electrical energy in a usable form. Also, the direct utilization of the electrical energy of nuclear reactions may be much more readily controlled by electrical methods than may the conversion of nuclear energy to thermal energy.

The instant invention comprises improvements on the methods and systems disclosed and claimed in applicants copending U. S. application Serial No. 679,081, filed June 25, 1946, now Patent 2,517,120, August 1, 1950, which contemplates the use of collector electrodes for collecting the charged particle rays from a radioactive source, and means for applying the resultant unidirectional potential between the source and collector electrodes to a load. One of the improvements comprising the instant invention includes providing, as the collector system of the generator, a series of absorbing regions such as thin parallel grid-electrodes that are semi-transparent to the nuclear radiations. The electrodes are generally parallel to each other and are of such thinness and density that .those nearer the source of nuclear energy are 4 Claims. (Cl. 310-3) substantially transparent to the higher energy radiated particles. Another improvement comprises the providing of a plurality of semi-transparent electrodes and guard rings forming a part thereof to distribute the generated potential over the insulator portion of the generator.

Among the objects of the invention are to provide improved methods of and means for generating electrical energy in response to nuclear reactions. Another object is to provide improved methods of and means for utilizing the electrical energy in nuclear reactions for generating high unidirectional potentials. An additional object is to provide improved methods of and means for utilizing atomic energy for generating electrical energy. A still further object of the invention is to provide improved methods of and means for utilizing radioactive materials as sources of electrical energy.

Another object of the invention is to provide improved methods of and means for converting atomic energy directly to electrical energy in commercially usable forms. An additional object is to provide improved methods of and means for employing nuclear reactions to generate a plurality of relatively large electrical currents.

A further object is to provide improved methods and means for obtaining currents at difierent potentials from a single source of radioactive material. Another object is to provide improved methods of and means for distributing a plurality of generated potentials over the insulator portion of the generator.

The various features of the invention will be described herein by reference to the accompanying drawing in which Figure 1 is a schematic diagram of the basic embodiment of the invention disclosed in said copending application and including a simple, single unidirectional voltage generator; Figure 2 is a schematic diagram of the modification of said basic embodiment of the invention constituting the instant invention; Figure 3 is a typical energy distribution curve of a radioactive source showing the relation of the number of emitted particles corresponding to various energy values of the particles expressed in equivalent volts; and Figure 4 is a graph showing the relation between the current in the external load circuit of the generator for a value of the resistance in the load circuit.

Similar reference characters are applied to similar elements throughout the drawing.

Referring to the drawing, Figure 1 illustrates the simplest form of the invention disclosed in said copending application and included herein for the purpose of describing the principles and operation of the system comprising a unidirectional high voltage generator I. The generator i includes a source 2 of alpha-rays, betarays or other charged particles derived from a quantity of radioactive material. A suitable a1- pha-ray radioactive source may comprise, for example, a quantity of polonium (84Po210). Likewise, a suitable beta-ray source may comprise a suitable quantity of radioactive phosphorus (15P32). Radioactive phosphorus is a pure beta-ray emitter which becomes stable after emission. It is thus suitable for use as a nucleonic power source since it emits no gaseous decay products and, therefore, it is suitable for vacuum applications.

The radioactive source 2 is surrounded, for example, by a spherical highly evacuated conductive collector electrode 3 having an aperture insulator 4 therein for a suitably insulated terminal 5 for the radioactive source 2. A load 6 is connected between the collector electrode 3 and the source terminal 5. If desired, the collector electrode 3 may be grounded as at i.

In operation, and in the absence of a load, beta particles (electrons) emitted by the radioactive source 2 travel to the collector electrode 3 and. charge it negatively as indicated by the dash line arrow 8. The charge upon the collector electrode 3 is negative with respect to the source 2 and increases until the potential of the collector electrode is sufficiently high to repel additional electrons arriving from the source 2, as shown by the dash line arrow 9. If it is assumed that the radioactive source 2 emits 1 m. e. v. electrons (beta rays), the potential of the collector electrode 3 would reach one m. e. v.

and would be negative with respect to the radioactive source. If a load is connected between the collector electrode 3 and the source terminal 5, a current will flow through the load and power will be dissipated therein. Thus the radioactive energy emitted in the beta-rays may be employed directly in its original electrical form to provide electrical energy.

If desired, an alpha-particle source may be employed instead of a beta-particle source, in which case the collector electrode 3 will be charged positively until it reaches a potential sufiiciently high to repel additional alpha particles. In such a modification of the invention, the collector electrode 3 becomes the positive terminal and the radioactive source 2 the negative terminal of the generator.

Referring to Figure 2, there is provided the generator l which consists of an envelope comprising a metal hollow portion I closed at one end and open at the other end to join with the open end of the insulator portion ll. Through the insulator end of the envelope passes the terminal which supports the radioactive source 2 adjacent the closed end of the metal portion of the envelope. The other end of terminal 5 is connected to ground as at I through the load 6. Metal envelope portion It may be grounded as at '4.

Inside the envelope and parallel to the walls thereof are a plurality of collector elements or regions, which may be in the form of thin metal sheets or fine grids of suitable material such as aluminum. These regions are semi-transparent to the radiations from source 2. In the dis-- closed embodiment, three collectors, 3a, 3b and 3c, are shown. It will be understood, however, that the plurality of collectors is not limited to three. These collectors are held in position at their closed ends by any conventional means (not shown). They are held in position at their open ends by being bent outward and connected to guard rings I2a, 12b and I20, respectively which pass through the glass portion ll of the envelope. By making these collectors of different lengths along the axis of the envelope, the potentials generated on the electrodes are distributed over the insulator portion ll. These guard rings also are the terminals for the load circuits, which include resistances 6a, 6b, and 60, respectively. These load resistances are also connected to ground as at I. Should it be desired to use the potential difference between any two collectors in an external circuit, the resistance load such as shown at l3 may be connected to collector guards [2b and I20.

Should it be desired to shield the insulation portion H of the envelope from the rays from the radioactive source 2, a heavy shield may be positioned above source 2, as shown at M.

By selecting the material of the radioactive source and the thickness of the collectors a wide variety of desired voltages and currents for various resistance load conditions may be satisfied. The maximum and minimum energies in the particles of the radiations as well as the average number of particles at individual ener y levels are known for the various radioactive elements in the form of energy distribution or spectrum curves. A typical energy distribution curve is shown in Figure 3. Likewise, the materials to be used and thinness of the collectors to make them transparent to particles of various energy levels and opaque to other energy levels particles are known.

In operation: As the radiation from source 2 is in the form of a stream of electrically charged particles, the potential to which an individual collector will rise with no flow of current therefrom will depend upon the number of particles that reach and are absorbed by that individual collector. If the first collector is relatively thin and reaches the potential V1 (see Figure 3) particles of less energy than V1, measured in electron volts, will be repelled (see arrow 9, Figure 1) and particles having sufiicient energy to penetrate and to pass through the collector will not be absorbed by and will contribute no charge to. the collector. Each collector will, therefore, absorb particles over a band of electro-volt values, which is represented in Figure 3 as the distance V'1-V1 in the abscissa axis, the thicker the collector and the denser the collector material the wider will be the band V'1-V1 and the more particles will be absorbed. As the height of the curve above the abscissa axis in Figure 3 is proportional to the number of charged particles emitted at the corresponding energy, cV, the area of the shaded portion of Figure 3 represents the current flowing to the collector from the radioactive source.

If the collectors comprise very fine mesh grids, some particles will pass through the grid open: ings, whereas most of the others will be stopped by the grid wires in the same manner as when thin solid collectors are used. This would result in a collector having much the same effective absorption as with solid collectors.

The potential to which the collector will risein state of equilibrium is given by the equation V equals Ri where R is the resistance between the collector and ground and i is the current collected by the collector. The resistance R may be the leakage resistance of insulation portion H or, in addition thereto, a load resistance inserted, as to connected between collector 3b and ground i.

In the practical cases band V1V1 will be narrow and hence the current spectrum collected by an individual collector will be of the same shape as the energy distribution curve. The current spectrum for collector 3a is plotted in Figure 4. The relation of the current in the external circuit for potentials of the collector, is plotted as a straight line, the slope of which is l/R, where R is the resistance between the grid and the ground.

It is apparent that similar curves may be plotted for the potential and current conditions for the other of the plurality of collectors. The shape of these current-potential curves for individual collectors will depend upon the thickness of the collectors through which the particles have passed and the energy distribution spectrum of the radioactive source, as the current flowing from the individual collectors is dependent upon the number of particles that reach the collector and are absorbed by the collector. In general, the curves defining the current-potential relations of collectors will be flatter for the collectors farther away from the radioactive source.

There is thus provided a unique method of and means for generating a plurality of electric potentials for use in external circuits and for providing a controlled gradient of potentials over the insulator portion of the nuclear generator.

I claim as my invention:

1. Apparatus for generating a plurality of electric energies including: an evacuated envelope including a metal portion and an insulation portion, a radioactive material disposed adjacent said metal portion and providing a source of charged particle emission, means semi-transparent to said emission disposed in regions adjacent to and successively more remote from said source for collecting said emitted particles to establish a plurality of potentials with respect to said source and to ground, means for shielding said insulation portion from said source, and means for utilizing said potentials.

2. Apparatus for generating a plurality of electric energies including: an evacuated envelope including a metal portion and an insulation portion, aradioactive material disposed adjacent said metal portion and providing a source of charged particle emission, means semi-transparent to said emission disposed in regions ad jacent to and successively more remote from said source for collecting said emitted particles to establish a plurality of potentials with respect to said source and to ground, the said collecting means extending through said insulation portion at predetermined spaced intervals along said in sulation portion whereby the potential gradient over the insulation portion is controlled, and means for utilizing said potentials.

3. Apparatus for generating a plurality of electric energies including: an evacuated envelope including a metal portion and an insulation portion, a radioactive material disposed adjacent said metal portion and providing a source of charged particle emission, means semi-transparent to said emission disposed in regions adjacent to and successively more remote from said source for collecting said emitted particles to establish a plurality of potentials with respect to said source and to ground, the said collecting means extending through and protruding beyond said insulation portion at spaced intervals along said insulation portion whereby the protrusions of said collectors form guard rings and connecting terminals for said potentials, and means for utilizing said potentials.

4. Apparatus according to claim 3 including means for shielding said insulation portion from said source.

ERNEST G. LINDER.

References Cited in the file of this patent UNITED STATES PATENTS Number 

